Cryptographic systems are known in the data processing art. In general, these systems operate by performing an encryption operation on a plain-text input message, using an encryption key, and a symmetric key block cipher, producing a cipher-text message. The encrypted message may then be sent over an unreliable and insecure channel to a receiver who shares the secret key. The receiver of the encrypted message performs a corresponding decryption operation, using the same key to recover the plain-text block. Because the same key is used by both the sender and receiver of the message, the process is referred to as a “symmetric key” process.
There is a related issue of message integrity. To elaborate, although the receiver of the cipher-text message can decrypt the cipher-text, the receiver is not assured that the cipher-text was not accidentally or maliciously altered during transmission. To ensure message integrity, the cipher-text message come accompanied with a message authentication code (MAC). This MAC is generated by the sender from the cipher-text using a cryptographic hash function.
Usually, the total computational time spent on encrypting the message is of the same order of magnitude as the time spent computing the subsequent MAC. Thus, two passes of equal duration are required to produce a cipher-text message along with its integrity assuring MAC.
Other ways have been described to achieve message integrity along with encryption. In these ways, a few extra steps of preparing a new random sequence are taken. The generated random sequence is then embedded into the cipher-text, and that is claimed to assure message integrity. The advantage of these alternatives over the MAC is that the extra steps taken are far fewer than required for computing the MAC.
Among the other ways, one requires two extra steps, and another requires just one extra step. However, the latter is less secure than schemes using a MAC. Thus, there is a tradeoff in performance.